linux-kernel - Re: [PATCH v2 0/4] dma-buf: document revoke mechanism to invalidate shared buffers

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Message-ID: <20260119075229.GE13201@unreal>
Date: Mon, 19 Jan 2026 09:52:29 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
Cc: Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	Alex Deucher <alexander.deucher@....com>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Gerd Hoffmann <kraxel@...hat.com>,
	Dmitry Osipenko <dmitry.osipenko@...labora.com>,
	Gurchetan Singh <gurchetansingh@...omium.org>,
	Chia-I Wu <olvaffe@...il.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Lucas De Marchi <lucas.demarchi@...el.com>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Jason Gunthorpe <jgg@...pe.ca>, Kevin Tian <kevin.tian@...el.com>,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	Alex Williamson <alex@...zbot.org>, linux-media@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
	linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
	virtualization@...ts.linux.dev, intel-xe@...ts.freedesktop.org,
	linux-rdma@...r.kernel.org, iommu@...ts.linux.dev,
	kvm@...r.kernel.org
Subject: Re: [PATCH v2 0/4] dma-buf: document revoke mechanism to invalidate
 shared buffers

On Sun, Jan 18, 2026 at 03:16:25PM +0100, Thomas Hellström wrote:
> Hi, Leon,
> 
> On Sun, 2026-01-18 at 14:08 +0200, Leon Romanovsky wrote:
> > Changelog:
> > v2:
> >  * Changed series to document the revoke semantics instead of
> >    implementing it.
> > v1:
> > https://patch.msgid.link/20260111-dmabuf-revoke-v1-0-fb4bcc8c259b@nvidia.com
> > 
> > ---------------------------------------------------------------------
> > ----
> > This series documents a dma-buf “revoke” mechanism: to allow a dma-
> > buf
> > exporter to explicitly invalidate (“kill”) a shared buffer after it
> > has
> > been distributed to importers, so that further CPU and device access
> > is
> > prevented and importers reliably observe failure.
> > 
> > The change in this series is to properly document and use existing
> > core
> > “revoked” state on the dma-buf object and a corresponding exporter-
> > triggered
> > revoke operation. Once a dma-buf is revoked, new access paths are
> > blocked so
> > that attempts to DMA-map, vmap, or mmap the buffer fail in a
> > consistent way.
> 
> This sounds like it does not match how many GPU-drivers use the
> move_notify() callback.

No change for them.

> 
> move_notify() would typically invalidate any device maps and any
> asynchronous part of that invalidation would be complete when the dma-
> buf's reservation object becomes idle WRT DMA_RESV_USAGE_BOOKKEEP
> fences.

This part has not changed and remains the same for the revocation flow as well.

> 
> However, the importer could, after obtaining the resv lock, obtain a
> new map using dma_buf_map_attachment(), and I'd assume the CPU maps
> work in the same way, I.E. move_notify() does not *permanently* revoke
> importer access.

This part diverges by design and is documented to match revoke semantics.  
It defines what must occur after the exporter requests that the buffer be  
"killed". An importer that follows revoke semantics will not attempt to call  
dma_buf_map_attachment(), and the exporter will block any remapping attempts  
regardless. See the priv->revoked flag in the VFIO exporter.

In addition, in this email thread, Christian explains that revoke
semantics already exists, with the combination of dma_buf_pin and
dma_buf_move_notify, just not documented:
https://lore.kernel.org/all/f7f1856a-44fa-44af-b496-eb1267a05d11@amd.com/

Thanks

> 
> /Thomas
> 
> 
> > 
> > Thanks
> > 
> > Cc: linux-media@...r.kernel.org
> > Cc: dri-devel@...ts.freedesktop.org
> > Cc: linaro-mm-sig@...ts.linaro.org
> > Cc: linux-kernel@...r.kernel.org
> > Cc: amd-gfx@...ts.freedesktop.org
> > Cc: virtualization@...ts.linux.dev
> > Cc: intel-xe@...ts.freedesktop.org
> > Cc: linux-rdma@...r.kernel.org
> > Cc: iommu@...ts.linux.dev
> > Cc: kvm@...r.kernel.org
> > To: Sumit Semwal <sumit.semwal@...aro.org>
> > To: Christian König <christian.koenig@....com>
> > To: Alex Deucher <alexander.deucher@....com>
> > To: David Airlie <airlied@...il.com>
> > To: Simona Vetter <simona@...ll.ch>
> > To: Gerd Hoffmann <kraxel@...hat.com>
> > To: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> > To: Gurchetan Singh <gurchetansingh@...omium.org>
> > To: Chia-I Wu <olvaffe@...il.com>
> > To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
> > To: Maxime Ripard <mripard@...nel.org>
> > To: Thomas Zimmermann <tzimmermann@...e.de>
> > To: Lucas De Marchi <lucas.demarchi@...el.com>
> > To: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
> > To: Rodrigo Vivi <rodrigo.vivi@...el.com>
> > To: Jason Gunthorpe <jgg@...pe.ca>
> > To: Leon Romanovsky <leon@...nel.org>
> > To: Kevin Tian <kevin.tian@...el.com>
> > To: Joerg Roedel <joro@...tes.org>
> > To: Will Deacon <will@...nel.org>
> > To: Robin Murphy <robin.murphy@....com>
> > To: Alex Williamson <alex@...zbot.org>
> > 
> > ---
> > Leon Romanovsky (4):
> >       dma-buf: Rename .move_notify() callback to a clearer identifier
> >       dma-buf: Document revoke semantics
> >       iommufd: Require DMABUF revoke semantics
> >       vfio: Add pinned interface to perform revoke semantics
> > 
> >  drivers/dma-buf/dma-buf.c                   |  6 +++---
> >  drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c |  4 ++--
> >  drivers/gpu/drm/virtio/virtgpu_prime.c      |  2 +-
> >  drivers/gpu/drm/xe/tests/xe_dma_buf.c       |  6 +++---
> >  drivers/gpu/drm/xe/xe_dma_buf.c             |  2 +-
> >  drivers/infiniband/core/umem_dmabuf.c       |  4 ++--
> >  drivers/infiniband/hw/mlx5/mr.c             |  2 +-
> >  drivers/iommu/iommufd/pages.c               | 11 +++++++++--
> >  drivers/vfio/pci/vfio_pci_dmabuf.c          | 16 ++++++++++++++++
> >  include/linux/dma-buf.h                     | 25
> > ++++++++++++++++++++++---
> >  10 files changed, 60 insertions(+), 18 deletions(-)
> > ---
> > base-commit: 9ace4753a5202b02191d54e9fdf7f9e3d02b85eb
> > change-id: 20251221-dmabuf-revoke-b90ef16e4236
> > 
> > Best regards,
> > --  
> > Leon Romanovsky <leonro@...dia.com>
> > 
>